All I know is that after you quench it is best to draw it back further than a knife blade - back to about 45 or 50 Rockwell if I am not mistaken?(anyone can correct me) This is because 55-60 is too hard for the pounding an axe takes and it is likely to chip or break. Again, up for interpretation and or correction on this.
As my own devils advocate, I would think one of those sweet double head axes on the Stihl lumberjack challenge would be made much harder to take a nasty edge that stays put but I am guessing your goal is not competition double headers?
Bob Urban